Transportation and storage of hydrocarbon fuels (e.g., gasoline) contribute to a significant amount of fuel lost to evaporation. In view of the rising need to conserve energy resources and the environmental impact associated with hydrocarbon vapors, there are presently far-reaching concerns about the economic loss and environmental impact from such fuel vapor emission. In addition, vapors generated from residual fuel, such as leftover puddles, in any vessel that requires maintenance or inspection represent a significant safety hazard to personnel working on that vessel. Hazardous flammable or toxic fumes also represent a commonplace danger to maintenance and/or inspection personnel because fuel must often be removed from the vessel before work can be performed, leaving the vessel filled with fumes.
Many surfactants and mixtures have been applied to liquid surfaces or other surfaces with absorbed and/or adsorbed liquids to reduce the evaporation rate of the liquid. In particular, one to several monolayers of close-packed linear surfactants have been added to water surfaces to reduce evaporation. Due to the high surface tension of water, surfactants can spread over the surface to reduce surface tension. Liquid hydrocarbons, on the other hand, typically have much lower surface tension, and hydrocarbon-based surfactants typically cannot spread across these liquid surfaces. Because of this, fluorosurfactants or trisiloxane surfactants are typically added in order to facilitate spreading on the surface. However, surfactants containing silicon and fluorine are known to generally present greater health and environmental hazards as compared to hydrocarbon-based surfactants. Some methods to encourage spreading of surfactants on low—surface tension surfaces involve fuel additives where surfactants are mixed with the bulk fuel. To achieve a layer on the surface of the bulk fuel in cases where physical mixture is the method of application, the state-of-the-art to date has required a surfactant having a lower density than the fuel, which allows the surfactant to assemble at gas/liquid interface, or the use of a surfactant containing an element such as fluorine or silicon that reduces the surface tension of the fuel.
And yet other surfactants that are applied directly to the surface of liquids, such as fuels, tend to contaminate or spoil the fuel. Currently, surfactant compositions are often applied to vessel surfaces by standard spray nozzles or cannons to physically mix with any remaining liquid and coat all surfaces. Such methods reduce the evaporation rate, but this inefficient use of the surfactant composition derives higher cost and higher contamination of the vessel, requiring cleaning before the vessel can be re-filled with liquid. Contamination of the liquid is particularly important when considering reducing the evaporation rate of bulk liquid hydrocarbons during transport or storage.
To accomplish minimal contamination while reducing evaporation rate as in the manner described above, the surfactant composition must be able to spread on the surface of a bulk liquid hydrocarbon. Since liquid hydrocarbons typically have a much lower surface tension than water, the surfactant composition may be required to contain special surfactants with fluorine or silicon as part of the surfactant chemical structure. When standard methods such as ordinary spray nozzles are used to apply this type of surfactant mixture, the special surfactants enable some droplets to spread on the liquid surface to form a layer to reduce evaporation. Even so, such methods and compositions often result in over-application from larger droplets sinking to the bottom of the liquid due to their higher density. This results in higher contamination and inefficient use of the surfactant mixture. Moreover, in cases where the evaporating surface area is not a continuous liquid surface such as a vessel drained of fuel, standard application methods of a surfactant composition such as spray nozzles must be able to reach all surfaces which is often not possible in large tanks or tanks with internal structure such as baffling. This results in poor coverage and higher evaporation rates.
Thus, there is a need in the art for methods and compositions that can reduce the evaporation of bulk liquids and/or liquids absorbed and/or adsorbed on various surfaces.